Methods for formation of recessed encapsulated microelectronic devices

ABSTRACT

A method for manufacturing microelectronic device packages. In one embodiment, the device package can include a support member having a first surface, a second surface facing opposite the first surface and a cavity extending through the support member from the first surface to the second surface. A microelectronic device is disposed in the cavity and is supported in the cavity with a removable retention member. The microelectronic device is electrically coupled to the support member and is partially surrounded with an encapsulating material. The removable retention member is then removed to expose a surface of the microelectronic device. Accordingly, the package can have a low profile because the encapsulating material does not surround one of the microelectronic device surfaces. In one embodiment, a heat conductive material can be engaged with the exposed surface of the microelectronic device to increase the rate at which heat is transferred away from the microelectronic device.

This application is a divisional of U.S. patent application Ser. No.09/606,428, filed on Jun. 28, 2000, now U.S. Pat. No. 6,576,494, issuedJun. 10, 2003.

TECHNICAL FIELD

This invention relates to recessed encapsulated microelectronic devices,and methods for forming such encapsulated devices.

BACKGROUND OF THE INVENTION

Packaged microelectronic assemblies, such as memory chips andmicroprocessor chips, typically include a microelectronic device mountedto a substrate and encased in a plastic protective covering. The deviceincludes functional features, such as memory cells, processor circuitsand interconnecting circuitry. The device also typically includes bondpads electrically coupled to the functional features. The bond pads arecoupled to pins or other types of terminals that extend outside theprotective covering for connecting the microelectronic device to buses,circuits and/or or other microelectronic assemblies.

In one conventional arrangement, shown in FIG. 1, a packaged device 50includes a substrate 10 (such as a printed circuit board or “PCB”)having an upper surface 11 and a lower surface 12. The substrate 10includes conductive substrate pads 14 on the upper surface 11 connectedto ball pads 15 on the lower surface 12 by a plurality of vias 16. Amicroelectronic die 30 having die bond pads 31 is positioned on theupper surface 11, and the die bond pads 31 are connected with to thesubstrate pads 14 by wire bonds 32. The microelectronic die 30 is thenencapsulated with an encapsulating material 40 to protect the die 30 andthe wire bonds 32. Solder balls can then be connected to the ball pads15 for linking the die 30 to a circuit or another device.

In another conventional arrangement, shown in FIG. 2, a package 50 a caninclude a lead frame 25 having lead fingers 27 positioned adjacent tothe die 30. In one aspect of this arrangement, the lead frame 25 caninclude a paddle (not shown) that extends between the lead fingers 27 tosupport the die 30. Alternatively, the paddle can be replaced with alayer of thermoset adhesive material 17 that extends between the leadfingers 27 and supports the die 30. The thermoset material 17 is thenheated to bond the material to the die 30, and the bond pads 31 on thedie 30 are wire bonded to the lead fingers 27. An encapsulating material40 a is disposed over both the die 30 and the thermoset material 17 toform the package 50 a, and the ends of the lead fingers 27 are bent toform pins 26 for connecting the die 30 to other devices or circuits.

The packages 50 and 50 a described above with reference to FIGS. 1 and 2can suffer from several drawbacks. For example, the overall height H ofthe packages 50 and 50 a may be so large that it is difficult tointegrate the packages with low-profile electronic products, such asmobile telephones and hand-held or laptop computers. Furthermore, it maybe difficult to transfer heat from the dies 30 because the dies 30 aresurrounded on all sides by materials having low thermal conductivities.For example, the die 30 shown in FIG. 1 is surrounded by theencapsulating material 40 and the substrate 10, and the die 30 shown inFIG. 2 is surrounded by the encapsulating material 40 a and thethermoset material 17. It is particularly important to dissipate heat inhigh-speed microprocessors and memory devices to maintain theperformance levels of these devices. Thus, the package 50 and 50 a maynot be adequate for use in many types of products.

SUMMARY

The present invention is directed toward microelectronic device packagesand methods for forming such packages. A method in accordance with oneaspect of the invention includes positioning a microelectronic device atleast partially within a cavity of a support member having a firstsurface and a second surface facing opposite the first surface, with thecavity extending through the support member from the first surface tothe second surface. The method can further include supporting themicroelectronic device relative to the cavity with a removable retentionmember. The microelectronic device is electrically coupled to thesupport member and a portion of the microelectronic device is encasedwith an encapsulating material. The removable retention member is thenremoved from the support member.

In a further aspect of the invention, the microelectronic device has afirst face and a second face facing opposite the first face. The secondface of the microelectronic device is initially engaged with theremovable retention member and is exposed when the removable retentionmember is removed. In still a further aspect of the invention, a heattransfer material can be applied to the second face of themicroelectronic device to conduct heat away from the microelectronicdevice.

The invention is also directed toward a microelectronic device package.In one aspect of the invention, the package can include a support memberhaving a first surface, a second surface facing opposite the firstsurface, and a cavity extending through the support member from thefirst surface to the second surface. The support member defines a firstregion extending outwardly from the first surface and a second regionextending outwardly from the second surface. A microelectronic devicehaving a first face and a second face facing opposite the first face isdisposed in the cavity. The package further includes an encapsulatingmaterial positioned in the first region defined by the support member,but not in the second region, such that the encapsulating material atleast partially surrounds the microelectronic device adjacent to thefirst face of the microelectronic device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially schematic, cross-sectional side elevational viewof a microelectronic die package in accordance with the prior art.

FIG. 2 is a partially schematic, cross-sectional side elevational viewof a another microelectronic die package in accordance with the priorart.

FIGS. 3A-3F are partially schematic, cross-sectional side elevationalviews depicting a process for forming a packaged microelectronic devicein accordance with an embodiment of the invention.

FIG. 4 is a partially schematic, cross-sectional side elevational viewof a packaged microelectronic device in accordance with anotherembodiment of the invention.

FIGS. 5A-5D are partially schematic, cross-sectional side elevationalviews depicting a process for forming a packaged microelectronic devicein accordance with still another embodiment of the invention.

DETAILED DESCRIPTION

The present disclosure describes packaged microelectronic devices andmethods for packaging such devices. Many specific details of certainembodiments of the invention are set forth in the following descriptionand in FIGS. 3A-5D to provide a thorough understanding of theseembodiments. One skilled in the art, however, will understand that thepresent invention may have additional embodiments, or that the inventionmay be practiced without several of the details described below.

FIGS. 3A-3E illustrate a method for forming a microelectronic devicepackage in accordance with an embodiment of the invention. Referringfirst to FIG. 3A, the package can include a support member 110, such asa PCB, having an upwardly facing upper surface 111 and a downwardlyfacing lower surface 112. In one aspect of this embodiment, the supportmember 110 can have a thickness of from about 100 microns to about 3,175microns. The support member 110 can have other suitable thicknesses inother embodiments. In another aspect of this embodiment, the supportmember 110 can be formed from a polyimide, BCB, FR4, bismalimidetriazine, or another suitable material.

The support member 110 can have support member pads 114 positioned onthe upper surface 111 and connected with vias (not shown) to ball pads115 that are also positioned on the upper surface 111. In anotherembodiment, the support member 110 can have other bond pads or terminalsfor coupling to a microelectronic device. In either embodiment, thesupport member 110 further includes a cavity 113 that extends throughthe entire support member 110 from the upper surface 111 to the lowersurface 112. Accordingly, the cavity 113 includes an upper opening 118at the upper surface 111 and a lower opening 119 at the lower surface112.

Referring now to FIG. 3B, a releasable retention member or cover 160 isreleasably attached to the lower surface 112 of the support member 110.In one aspect of this embodiment, the retention member 160 includes anadhesive layer that is releasably adhered to the lower surface 112 ofthe support member 110.

For example, the retention member 160 can include a pressure-sensitiveadhesive that attaches the retention member 160 to the support member110. In a further aspect of this embodiment, the adhesive can be ahigh-temperature adhesive for use in subsequent processing steps (suchas high temperature wire bonding) that subject the adhesive to elevatedtemperatures. Alternatively, the adhesive can be a room-temperatureadhesive for use in subsequent processing steps that do not subject theadhesive to significantly elevated temperatures. Suitable adhesives forboth embodiments are available from 3M of St. Paul, Minn.

Alternatively, the retention member 160 can include an adhesive that isactivated and/or released by methods other than applying pressure. Forexample, the adhesive can be a radiation-sensitive adhesive that bondsto the lower surface 112 and/or detaches from the lower surface 112 uponexposure to radiation at a selected wavelength. In another embodiment,the adhesive can be temperature sensitive (e.g., a thermoplastic)adhesive. Accordingly, the adhesive can be heated and cooled toinitially adhere the retention member 160 to the microelectronic device,and then heated again to remove the retention member 160, as describedbelow with reference to FIG. 3E. In still another embodiment, theretention member 160 can be attached to the lower surface 112 by otherforces, such as electrostatic forces. In any of these embodiments, theretention member 160 extends over all or a portion of the lower opening119 of the cavity 113 in the support member 110. For example, theretention member 160 can include a solid film or, alternatively, theretention member 160 can be perforated, so long as at least a portion ofthe retention member 160 extends over at least a portion of the loweropening 119.

Referring now to FIG. 3C, a microelectronic device 130, such as a DRAMchip or microprocessor chip, is positioned in the cavity 113. Themicroelectronic device 130 has an upper face 133 with device bond pads131, and a lower face 134 opposite the upper face 133. Themicroelectronic device 130 is supported relative to the cavity 113 bythe retention member 160. For example, when the retention member 160includes an adhesive, the adhesive engages the lower face 134 of themicroelectronic device 130 and at least restricts movement of themicroelectronic device 130 relative to the support member 110. Themicroelectronic device 130 is then electrically coupled to the supportmember 110 by attaching wire bonds 132 between the device bond pads 131on microelectronic device 130 and the support member pads 114 on thesupport member 110.

In one aspect of this embodiment, the microelectronic device 130 isslightly smaller than the cavity 113, such that the perimeter ofmicroelectronic device 130 is spaced apart from the walls of the cavity113 by a gap 135. In another aspect of this embodiment, themicroelectronic device 130 has a thickness between the upper face 133and the lower face 134 of about 500 microns, and in other embodiments,this thickness can be greater or less than 500 microns. Accordingly, theupper face 133 can be flush with the upper surface 111 of the supportmember 110, or the upper face can project above or below the uppersurface 111. The position of the upper face 133 relative to the uppersurface 111 depends on the thickness of the microelectronic device 130and the thickness of support member 110. However, in any of theseembodiments, the lower face 134 is generally flush with the lowersurface 112 of the support member 110.

Referring now to FIG. 3D, the microelectronic device 130 is encapsulatedby disposing an encapsulating material 140 over the microelectronicdevice 130 and a portion of the upper surface 111 of the support member110. The encapsulating material 140 can fill in the gap 135 (FIG. 3C)between the microelectronic device 130 and the walls of the cavity 113.The encapsulating material 140 can be an epoxy or other generallynon-conductive, conformal material.

In one aspect of an embodiment shown in FIG. 3D, the support member 110defines an upper region 120 extending outwardly away from the uppersurface 111 and a lower region 121 extending outwardly away from thelower surface 112. Because the retention member 160 is positionedtightly against the lower surface 112, the encapsulating material 140extends only into the upper region 120 and into the gap 135, but theencapsulating material 140 does not extend into the lower region 121. Asa result, the lower face 134 of the microelectronic device 130 remainsfree of the encapsulating material 140.

Referring now to FIG. 3E, the removable retention member 160 is releasedor removed from the lower surface 112 of the support member 110 toexpose the lower surface 112 of the support member 110 and the lowerface 134 of the microelectronic device 130. The resultingmicroelectronic device package 150 can then be singulated from otherpackages (not shown) on the same support member 110 and then coupled toanother device. For example, in one embodiment shown in FIG. 3F, thepackage 150 can be coupled with solder balls 122 to another supportmember 110 a in a board-over-chip (“BOC”) configuration. In a furtheraspect of this embodiment, a heatsink 170 can be coupled to the exposedlower face 134 of the microelectronic device 130 to increase the rate atwhich heat is dissipated from the microelectronic device 130. Forexample, the heat sink 170 can include silicon nitride or anothermaterial having a greater thermal conductivity than the encapsulatingmaterial 140. Alternatively, the lower face 134 can remain exposed toincrease the rate at which heat is transferred by convection away fromthe device 130. In either embodiment, the rate at which heat istransferred away from the microelectronic device 130 can be greater thanthe conventional arrangement in which the lower face 134 of themicroelectronic device 130 is covered with an encapsulating material.

One feature of an embodiment of the method and package 150 describedabove with reference to FIGS. 3A-3F is that on overall thickness T (FIG.3E) of the package 150 is less than the thickness of a correspondingconventional package. The thickness is reduced because themicroelectronic device 130 is recessed in the support member 110 andbecause there is no encapsulating material 140 on the underside of thepackage 150. For example, thickness T can be 1400 microns or less in oneembodiment with the microelectronic device 130 projecting 150-250microns or less above the upper surface 111 of the support member 110.An advantage of this feature is that the package 150 has a low profileand can more easily be used in compact devices, such a mobile telephonesand hand-held computing devices.

Another feature of an embodiment of the method and package 150 describedabove with reference to FIGS. 3A-3F is that the lower face 134 of themicroelectronic device 130 can remain exposed after the microelectronicdevice 130 is encapsulated. An advantage of this feature is that theheat transfer rate from the microelectronic device 130 can be increasedrelative a microelectronic device that is fully encapsulated.Accordingly, the microelectronic device 130 can operate at a lowertemperature to increase the lifespan and/or the reliability of themicroelectronic device 130.

FIG. 4 is a partially schematic, cross-sectional side elevational viewof a microelectronic device package 250 having a first support member110 coupled to a second support member 210 a in a ball grid array(“BGA”) arrangement in accordance with another embodiment of theinvention. In one aspect of this embodiment, the support members pads114 on the upper surface 111 of the first support member 110 areconnected with vias (not shown) to first ball pads 215 on the lowersurface 112 of the first support member 110. The second support member210 a has second ball pads 215 a aligned with the first ball pads 215. Asolder ball 222 extends between selected first ball pads 215 andcorresponding second ball pads 215 a to electrically couple themicroelectronic device 130 to the second support member 215 a. Asdescribed above with reference to FIG. 3F, the package 250 can include aheatsink 170 coupled to the lower face 134 of the microelectronic device130. The heatsink 170 can extend part-way to the second support member210 a, or can contact the second support member 210 a. Alternatively,the heatsink 170 can be eliminated to allow for convective heat transferdirectly from the lower face 134 of the microelectronic device 130.

FIGS. 5A-5B are partially schematic, cross-sectional side elevationalviews depicting a process for forming a packaged microelectronic devicein accordance with still another embodiment of the invention. Referringfirst to FIG. 5A, the package can include a support member 310 having afilm layer 324 with an upwardly facing upper surface 311 and adownwardly facing lower surface 312. A cavity 313 extends through thefilm layer 324 from the upper surface 311 to the lower surface 312. Atrace layer 323 having conductive traces extends over the cavity 313 andadjacent to the upper surface 311 of the film layer 324.

Referring now to FIG. 5B, the microelectronic device 130 is disposed inthe cavity 313 with the upper face 133 of the microelectronic devicecontacting the trace layer 323 and each device bond pad 131 contactingan individual trace of the trace layer 323. A retention member 360 isattached to the lower surface 312 of the film layer 324 to extend overpart or all of the cavity 313. The retention member 360 can attach tothe lower surface 312 by adhesive forces, electrostatic forces, or otherforces as described above with reference to FIG. 3B. The retentionmember 360 also attaches to the lower face 134 of the microelectronicdevice 130. Accordingly, the retention member 360 can hold themicroelectronic device 130 in place in the cavity 313 while a tab bondertool (not shown) connects the traces of the trace layer 323 to thedevice bond pads 131.

Referring now to FIG. 5C, an encapsulating material 340 is disposed onthe trace layer 323, the upper face 133 of the microelectronic device130, and the upper surface 311 of the film layer 324 to encapsulate themicroelectronic device 130. The support member 310 defines an upperregion 320 extending outwardly away from the trace layer 323, and alower region 321 extending outwardly away from the lower surface 312 ofthe film layer 324 in a manner generally similar to that described abovewith reference to FIG. 3D. Accordingly, the encapsulating material 340extends into the upper region 120 and into a gap 335 (FIG. 3B) betweenthe microelectronic device 130 and the walls of the cavity 313, but itdoes not extend into the lower region 121. When the retention member 360is removed (FIG. 5D), the resulting device package 350 protects andsupports the microelectronic device 130 while leaving the lower face 134of the microelectronic device 130 free of the encapsulating material340. Accordingly, the overall thickness of the package 350 can be lessthan that of corresponding conventional packages, and the rate at whichheat is transferred away from the microelectronic device 130 can beincreased relative to that of conventional packages.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

1. A method for packaging a microelectronic device having a first faceand a second face opposite the first face, comprising: positioning themicroelectronic device adjacent to a support member, the support memberincluding a generally non-conductive substrate carrying conductiveelements, the support member having a first surface, a second surfacefacing opposite the first surface and a cavity extending through thesupport member from the first surface to the second surface; disposingthe microelectronic device in the cavity such that the second face isapproximately flush with the second surface of the support member;encapsulating a portion of the microelectronic device in the cavity withan encapsulating material while temporarily covering the second face ofthe microelectronic device with a releasable cover adhesively attachedto the microelectronic device to at least restrict contact between theencapsulating material and the second face of the microelectronicdevice; and removing the releasable cover.
 2. The method of claim 1,wherein the releasable cover includes an adhesive layer, and wherein themethod further comprises: positioning the adhesive layer adjacent to thesecond surface of the support member with an adhesive portion of theadhesive layer extending over at least a portion of the cavity adjacentto the second surface of the support member; removably attaching theadhesive layer to the microelectronic device while the microelectronicdevice is positioned in the cavity and before at least partiallysurrounding the microelectronic device; and removing the adhesive layerfrom the support member and the microelectronic device after at leastpartially surrounding the microelectronic device with the encapsulatingmaterial.
 3. The method of claim 1, wherein removing the releasablecover includes exposing the second face of the microelectronic device.4. The method of claim 1, wherein the microelectronic device has a firstface engaged with the encapsulating material and a second face facingopposite the first face, and the encapsulating material has a first heattransfer coefficient, and wherein the method further comprises disposinga heat conductive material in direct contact with the second face of themicroelectronic device, the heat conductive material having a secondheat transfer coefficient higher than the first heat transfercoefficient.
 5. The method of claim 4, wherein disposing a heatconductive material includes positioning silicon nitride against thesecond face of the microelectronic device.
 6. The method of claim 1wherein positioning the microelectronic device adjacent to a supportmember includes positioning the microelectronic device adjacent to aprinted circuit board.
 7. A method for packaging a microelectronicdevice having a first face and a second face opposite the first face,comprising: positioning the microelectronic device adjacent to a supportmember, the support member having a first surface, a second surfacefacing opposite the first surface and a cavity extending through thesupport member from the first surface to the second surface; disposingthe microelectronic device in the cavity such that the second face isapproximately flush with the second surface of the support member;encapsulating a portion of the microelectronic device in the cavity withan encapsulating material while temporarily covering the second face ofthe microelectronic device with a releasable cover by applying anelectrostatic charge to a releasable cover; supporting themicroelectronic device relative to the cavity with the electrostaticcharge to at least restrict contact between the encapsulating materialand the second face of the microelectronic device; and removing thereleasable cover.
 8. A method for packaging a microelectronic device,comprising: positioning a microelectronic device proximate to a supportmember, the support member including a generally non-conductivesubstrate carrying conductive elements, the support member having afirst surface, a second surface facing opposite the first surface, acavity extending through the support member from the first surface tothe second surface, and an adhesive film adjacent to the second surfaceof the support member; disposing a microelectronic device in the cavity,the microelectronic device having a first face and a second face facingopposite the first face; engaging the second face of the microelectronicdevice with a portion of the adhesive film accessible through thecavity; electrically coupling the microelectronic device to the supportmember; partially surrounding the microelectronic device with anencapsulating material; and removing the adhesive film from the supportmember.
 9. The method of claim 8, wherein removing the film includesexposing the second face of the microelectronic device.
 10. The methodof claim 8, wherein the encapsulating material has a first heat transfercoefficient, and wherein the method further comprises disposing a heatconductive material in direct contact with the second face of themicroelectronic device, the heat conductive material having a secondheat transfer coefficient higher than the first heat transfercoefficient.
 11. The method of claim 10, wherein disposing a heatconductive material includes positioning silicon nitride against thesecond face of the microelectronic device.
 12. The method of claim 8,further comprising disposing the microelectronic device in the cavitywith the second face of the microelectronic device at leastapproximately flush with the second surface of the support member andthe first face of the microelectronic device approximately flush with orrecessed from the first surface of the support member.
 13. The method ofclaim 8, further comprising disposing the microelectronic device in thecavity with the second face of the microelectronic device at leastapproximately flush with the second surface of the support member andthe first face of the microelectronic projecting outwardly from thefirst surface of the support member.
 14. The method of claim 8 whereinpositioning the microelectronic device adjacent to a support memberincludes positioning the microelectronic device adjacent to a printedcircuit board.
 15. A method for transferring heat from a microelectronicdevice, comprising: positioning the microelectronic device adjacent to asupport member, the support member including a generally non-conductivesubstrate carrying conductive elements, the support member having afirst surface, a second surface facing opposite the first surface, and acavity extending through the support member from the first surface tothe second surface; disposing the microelectronic device in the cavitywith a first face of the microelectronic device facing opposite a secondface of the microelectronic device; supporting the microelectronicdevice relative to the cavity with a releasable adhesive member;electrically coupling the microelectronic device to the support member;removing the adhesive member; partially surrounding the microelectronicdevice and the support member with an encapsulating material bydisposing the encapsulating material adjacent to the microelectronicdevice in a first region extending outwardly from the first surface ofthe microelectronic device without coupling the encapsulating materialto the microelectronic device in a second region extending outwardlyfrom the second surface of the support member; directly engaging thesecond face of the microelectronic device with a heat conductivematerial having a heat transfer coefficient higher than a heat transfercoefficient of the encapsulating material; and dissipating heat from themicroelectronic substrate by transferring heat directly from the secondface of the microelectronic device to the heat conductive material. 16.The method of claim 15, wherein disposing a heat conductive materialincludes positioning silicon nitride against the second face of themicroelectronic device.
 17. The method of claim 15, further comprisingdisposing the microelectronic device in the cavity with the second faceof the microelectronic device at least approximately flush with thesecond surface of the support member and the first face of themicroelectronic device approximately flush with or recessed from thefirst surface of the support member.
 18. The method of claim 15, furthercomprising disposing the microelectronic device in the cavity with thesecond face of the microelectronic device at least approximately flushwith the second surface of the support member and the first face of themicroelectronic projecting outwardly from the first surface of thesupport member.
 19. The method of claim 15 wherein positioning themicroelectronic device adjacent to a support member includes positioningthe microelectronic device adjacent to a printed circuit board.